1. Field of the Invention
The present invention relates to a charging apparatus for charging a secondary battery used for an apparatus driven by electric power such as a video camera and a personal computer, and in particular, to a novel charging apparatus capable of charging a secondary battery independently of the use/non-use state of the apparatus.
2. Description of the Prior Art
An apparatus driven by electric power such as a video camera and a personal computer (having a circuit which will be referred to as a set circuit hereinafter) is provided with a secondary battery which is chargeable as a drive power source and may be provided further with a charging apparatus for charging this secondary battery.
FIG. 1 shows a conventional circuit configuration of such a charging apparatus. It should be noted that FIG. 1 shows a case when a set circuit 101 and a secondary battery 102 are provided as a unitary block of a set main body 103 which is connected to an AC adapter 104 for power supply. That is, in the example of FIG. 1, the AC adapter 104 is connected to an AC power input so that current from the AC adapter 104 as an external power source is converted by the AC adapter 104 into a predetermined constant current for supply to the set main body 103. Moreover, the AC adapter 104 in the circuit configuration of FIG. 1 shows an output characteristic shown in FIG. 2.
In the example of FIG. 1, the set circuit 101 is connected between an output terminal VI from the AC adapter 104 and a grounding terminal G1 so as to receive a power supply via the AC adapter 104 from the AC power source. On the other hand, at the side of the secondary battery 102 built in the set main body 103, there is provided a switch Sw1 between a minus terminal of the secondary battery 102 and the grounding terminal G1. This switch S1 is turned on only when a signal indicating a lower power consumption state or a non-operation state is transmitted from the set circuit 101 as shown by an arrow S1 in FIG. 1. That is, in this charging apparatus, the switch Sw1 is turned only when the set circuit 101 is in the lower power consumption state or non-operation state, for charging the secondary battery 102.
In order to prevent that an excess current as a charge current Ib is supplied to the secondary battery 102, the set circuit 101 transmits a signal indicating that the secondary battery 102 is being charged, via a terminal C1 to the AC adapter 104. When the AC adapter is supplied with the signal indicating that the secondary battery 102 is being charged, the AC adapter 104 controls the current supplied to the set main body 103, so as to be a predetermined current value appropriate for charging the secondary battery 102.
If the set circuit 101 is in a drive state, a signal indicating the drive of the set circuit 101 is transmitted from the set circuit 101 through the terminal C1 to the AC adapter 104. This signal drives a switch Sw2 connected to one of the terminals of a current control amplifier Amp2, and the other terminal of the current control amplifier Amp2 is supplied with a first reference voltage Ref1.
Here, when the first reference voltage Ref1 is supplied to the one of the current control amplifier Amp2, the total current Io supplied to the set main body 103 is a set circuit current Is which drives the set circuit 101, so as to control the output from the AC adapter 104 as shown by a solid line IS in FIG. 2. That is, the current supplied from the AC adapter 104 to the set main body 103 is controlled so that the total current Io supplied to the set main body 103 will not exceed the maximum current value ISmax which can be supplied to the set circuit 101.
On the other hand, when the set circuit 101 is in the low power consumption state or non-operation state, a signal indicating that the set circuit 101 is in the low power consumption state or non-operation state is transmitted from the set circuit 101 via the terminal C1 to the AC adapter 104. This signal causes to drive the switch Sw2 connected to one of the terminals of the current control amplifier Amp2 built in the AC adapter 104, so that the input to the other terminal of the current control amplifier Amp2 is a second reference voltage Ref2.
If the one of the terminals of the current control amplifier Amp2 is supplied with the second reference voltage Ref2, the total current Io supplied to the set main body 103 is a charge current Ib to the secondary battery 102, and the output of the AC adapter 104 is controlled so as to be indicated by a dotted line IB in FIG. 2. That is, the current supplied from the AC adapter 104 to the set main body 103 is controlled so that the total current Io supplied to the set main body 103 will not exceed the maximum current value IBmax which can be supplied to the secondary battery 102.
In the conventional charging apparatus having the aforementioned configuration, the secondary battery is not charged while the set circuit is driven. Consequently, in the conventional charging apparatus, when charging the secondary battery, it is necessary that the set circuit be in the lower power consumption state or non-operation state, which causes various inconveniences.
It should be noted that there is also a charging apparatus capable of the secondary battery when the set circuit is other than in the lower power consumption state or non-operation state. However, such a conventional charging apparatus has a very complicated circuit configuration and cost much.